1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Grounding on stainless steel chrome chassis?

Discussion in 'Shock Brother's DIY Amps' started by Outlaws, Jan 22, 2021.

  1. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    I am gonna build my 6th amp and haven’t used a chrome chassis yet. I guess I am going to have the brass plate for the preamp. Is chrome going to conduct well enough I can run my grounds like any of robs layouts without a further runner meeting back at single star?
    Just gonna be a 5F2Aish build but it’s cleaner to account for stuff ahead of time.
     
  2. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,124
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Why a brass plate? Brass on stainless, IIRC, corrodes even worse then brass on steel.

    Whose chassis are you using? With a Weber stainless chassis I just used star washers and keps nuts like I do on steel or alu. Stainless may be less conductive than they are but my simple split bus works fine.
     
    Outlaws and goonie like this.
  3. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    218
    Joined:
    Nov 23, 2020
    Location:
    Finland
    Chassis is electrically a "shield"!

    Do not use it on any operative electric circuit!

    Chassis also makes amp safer when it "burns" building mains fuse in case voltage "jumps" to chassis and this mechanism uses mains cable Earth wire which needs to be connected to chassis very near mains cable input or IEC connector. This is FIRST wire you need to connect to chassis!

    If your amplifier is simple and use up to three pre amp tubes using a Single Ground Bus is easiest way to build it. If more you could consider Star Grounding.

    Chassis protects circuit from electromagnetic noise which comes outside and Signal Ground bus is connected with chassis very close the input jack ot using metal jack. Electrically this is best place because input signal is lowest and impedance is high so least amount of noise gets absorbed. This is LAST connection to chassis!

    Building this way no operative current runs thru chassis and it is good because chassis is huge and if there runs current it spreads to circuits. Do not solder anything to potentiometer cases because they are shields and already have electrical connection with metal chassis. Use insulated loudspeaker jacks and connect OPT output coil to SG. If power amp has cathode power resistors they also get SG from SG bus.

    Signal Ground begins from input jack and collects all return currents and they go to either power transformer Center Tab where SGB ends and it is NOT connected to chassis! When SS bridge rectifier is used SG ends to its negative and it is insulated as well.
     
    tubelectron and FenderLover like this.
  4. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    Probably a Weber chassis. It has the brass plate for the input and controls.
    It’s chrome plated stainless, not a stainless. I guess my question was is a star washer good for grounding to a chrome chassis. Sounds like it is.
     
  5. schmee

    schmee Doctor of Teleocity

    Posts:
    13,941
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Well.....Damn! Someone should have told Leo Fender that! :eek:
     
  6. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,649
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Check continuity with your DMM!
     
  7. schmee

    schmee Doctor of Teleocity

    Posts:
    13,941
    Joined:
    Jun 2, 2003
    Location:
    northwest
    I'm not up to date, but at one point Weber went to polished stainless to avoid all the trouble they were having with a chrome plating source. Are you sure it's chromed SS? Makes no sense....
     
  8. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    I mean that’s what their site says. I’ll probably skip using theirs as they seem to not put any effort into their page. The speakers are great but they leave too much to the imagination in the amp parts section.
     
    schmee likes this.
  9. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    Btw, the 5F2A schematic has one thing I am not familiar with...

    what’s this on the speaker from the OT?
     

    Attached Files:

  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,124
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    That's basically just the speaker.

    EDIT: Also, I just looked at Weber's site and it looks to me like it's just polished stainless, no chrome involved. I may not be looking at what you're seeing, of course.

    My Weber chassis was fine, had a couple nice features in fact, but OTOH SS is a pain to drill. And no, you're right, the chassis and cab shops are not the Weber speaker shop. Even if you go with their chassis (it'd be strong, and nice looking I bet) there's no need to go with their layout or other details, especially the brass plate.
     
    Last edited: Jan 22, 2021
  11. dan40

    dan40 Friend of Leo's

    Posts:
    2,095
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    I have never noticed that extra line on the schematic before. Interesting!
     
  12. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    The extra line is not on any other 5f1 or non A 5f2. But.. Mojotones layout has this... which is why I even starting looking at this part. Insulate?
     

    Attached Files:

  13. Outlaws

    Outlaws Tele-Meister

    Posts:
    366
    Joined:
    Jan 16, 2007
    Location:
    None
    Ya I don’t think the Weber is saying chrome. Maybe it was someone else or I just assumed they chromed it. I am basically doing a mix match of everything to end up with a 10” 5F2A. I’ll get a different chassis as I don’t want to drill stainless anyways for moving the speaker jack. Will completely destroy the bit.
     
  14. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    218
    Joined:
    Nov 23, 2020
    Location:
    Finland
    Yes obviously someone should have! Perhaps he knew there was better way or did not know? Perhaps building amps cheaper and faster was better business? It does not mean We have to make same mistakes anymore! Also modern world has more electromagnetic noise than half a century ago.

    Please tell any advantage there is to run return current thru chassis?

    And now when you can't We understand You did not wan't to understand what I wrote. It is not perfect english and terms were not scientifically correct but overall there's the difference what should come between signal ground and shield/chassis.
     
  15. tubelectron

    tubelectron Tele-Afflicted

    Posts:
    1,742
    Joined:
    Nov 25, 2010
    Location:
    France
    I never do star GND. I make only one GND point to the chassis, placed close to the input, where the sensivity to adverse noise is the highest, to null any adverse noise difference of potential.

    I always use a ground bus in logical order, going from the PSU caps to the GND chassis point, collecting in order : PSU, power Stage, preamp stage, input stage, input with chassis GND point.

    For GND'ing a chrome plated chassis, I would simply put a bolt and a lug accross the amp input for the unique GND point.

    But it's me, OK ? :D

    -tbln.
     
    FenderLover and 2L man like this.
  16. trev333

    trev333 Telefied Ad Free Member

    Posts:
    26,254
    Joined:
    Dec 3, 2009
    Location:
    Coolum Beach,Australia
    my guess is it represents a speaker out jack that cuts the cab speaker out....
     
  17. FenderLover

    FenderLover Poster Extraordinaire

    Posts:
    5,823
    Joined:
    Jun 11, 2009
    Location:
    Minnesota
    I've been banging this drum for a long time, but this forum likes to use the split ground (ground loop) method. We just have to accept it and move on.

    Weber chassis is polished stainless. Use a star washer. Done.
     
  18. schmee

    schmee Doctor of Teleocity

    Posts:
    13,941
    Joined:
    Jun 2, 2003
    Location:
    northwest
    It's all good man. But reality is reality:
    I dont know the physics of why, but if you star ground the input preamp section to the power section in many tweed amps with a bridging wire, or with a star ground. It will hum loudly. If you separate the two, even though they are grounded through the chassis, it will be quiet. Been there done that. Perhaps using the chassis it becomes a grounded shield like shielding a guitar?

    A shielded guitar is another example where it works to reduce noise also. You are making the entire shielding system the ground plane.

    Based on my Ham Radio knowledge I would say the surface area of the ground plane is what reduces noise.
     
    2L man likes this.
  19. FenderLover

    FenderLover Poster Extraordinaire

    Posts:
    5,823
    Joined:
    Jun 11, 2009
    Location:
    Minnesota
    YMMV. Mine certainly does.
     
    sds1 likes this.
  20. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,882
    Joined:
    Dec 30, 2019
    Location:
    california
    It is a ground wire connecting the chassis and the speaker frame. The Harvard 6G10 schematic has it shown as well.

    I have read it is a throwback to when power transformers were mounted to the speaker frame. It may have been a safety ground.

    I have also read it is used on modern equipment. IMO it is snakeoil or sales gimmick. There is no fact based reason to ground the speaker frame. There is some talk of shielding microphones and shielding the speaker performs a similar function. It doesn't.

    I have read Fender used a wire from the chassis to the speaker frame on many Super Champs. ???
     
    dan40, Outlaws and Peegoo like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.